Mesopic increment detection sensitivity, Part I: Phenomenological analysis

Mesopic threshold detection sensitivity was investigated by projecting quasi-monochromatic incremental targets with 22 centroid wavelengths between 422 nm and 652 nm onto different backgrounds. Every detection target was observed by at least nine subjects under eight different viewing conditions: two mesopic luminance levels (0.1 cd/m2; 1 cd/m2) and four eccentricities of target appearance off the visual axis (0°, 2.65°, 10° and 20°). Results were expressed in terms of absolute detection sensitivity values, i.e. inverse increment radiance values for each target at the detection threshold in sr·m2·W−1 units. In this part, the experimental method is described, and the dataset is analysed in terms of retinal mechanisms.